Despite tremendous advances in medicine, breast cancer remains a leading cause of death in the United States as well as the rest of the world. It has been estimated that there will be 182,460 new cases and 40,480 deaths in the US in 2008 due to breast cancer in women. In view of the limited treatment options for patients with advanced stages of breast cancer, preventive control approaches, in particular chemoprevention could play an important role in therapeutic strategies to combat this disease. The plant-derived triterpenoids are used for medicinal purposes in many Asian countries, and some of these compounds are reported to have promising cancer-suppressive activity against various human breast cancer cells in vitro. Amooranin (AMR) is a triterpene acid isolated from the stem bark of Amoora rohituka, a well known medicinal plant native of India. AMR has been shown to inhibit the proliferation of human breast carcinoma cells in vitro as well as suppress rat mammary tumors in vivo. Recently, it has been shown that a novel synthetic analogue of amooranin (AMR-Me) has enhanced potency in the killing of human breast carcinoma cells in vitro because of its effects on genes associated with cell proliferation and apoptosis. This revised application is based on the hypothesis that AMR-Me would be clinically useful as a chemopreventive agent in human breast cancer. Accordingly, the objectives of this proposed research are to evaluate the chemopreventive effects of AMR-Me and to delineate its possible mechanism(s) of action in a well established, chemically-induced animal model of breast cancer, which closely mimics the human disease. Female Sprague-Dawley rats will be fed either a basal diet or diet supplemented with various levels of AMR-Me resulting in increasing doses of this terpenoid. The chemopreventive doses will be based on an experimentally-determined maximum tolerated dose (MTD). The AMR-Me treatment will start one week prior to a single oral (60 mg/kg) administration of 7,12-dimethylbenz(a)anthracene (DMBA), an established carcinogen for the initiation of mammary tumors. Animals will be palpated starting 4 weeks following DMBA administration to record the presence, location, and size of tumors. All animals will be sacrificed 18 weeks following the initiation of the mammary carcinogenesis with DMBA to conduct biological, biochemical, and molecular endpoint studies. The chemopreventive effect of AMR-Me will be assessed from the incidence, multiplicity, volume, and size distribution of mammary tumors. The influence of AMR-Me in modulating proliferation index, apoptotic index, and estrogen receptor expressions will be investigated. The possible mechanistic role of AMR-Me at the genetic and molecular pathways that lead to the induction of apoptosis and inhibition of cell proliferation will be thoroughly examined.